When an offshore coiled tubing operation is performed, often the coiled tubing equipment, such as the coiled tubing reel and the coiled tubing power stand, must be lifted off of a boat and transported to an area where an operation may be performed, such as an offshore platform. In many areas, each piece of equipment that is lifted is required to meet DNV lifting standards. Some DNV standards that cover lifting requirements for coiled tubing equipment are DNV 2.7-1, DNV 2.7-3, and RCLA (Rules for Certification of Lifting Appliances.) Each of these lifting standards, as worded on date of the filing of this application, is herein incorporated by reference.
DNV 2.7-1 and 2.7-3 provide requirements for the lifting of coiled tubing equipment that weighs up to 50,000 pounds. DNV 2.7-1 provides requirements for the lifting of “containers.” DNV 2.7-3 is a new standard enacted in April of 2006 that provides requirements for the lifting of “portable offshore Units that are not shaped like containers.” Above the 50,000 pound limit for DNV 2.7-1 and DNV 2.7-3, RCLA governs.
Each of the three standards require that all of the load carrying members and welds of the lifted equipment meet certain Charpy impact properties and pass a very high level of welding inspection. This inspection includes certifying the welding processes, the machines, the welders that perform the procedures, the Charpy impact properties of the as-deposited weld metal, and the joint fit-up. Also required is a visual inspection of all the welds, a non-destructive evaluation of the welds, load testing to certain (very high) prescribed levels, and a post lifting non-destructive evaluation of the welds. All of this combines to make any equipment certified to these standards extremely expensive relative to equipment built to standard engineering practices.
An additional complication is introduced by the ability to separate the coiled tubing reel from its accompanying power stand, the power stand being a stand that supports the reel and rotates it to make the coiled tubing thereon spool onto or off of the reel depending on the direction of rotation of the reel. Since the coiled tubing reel is one of the heaviest pieces of coiled tubing equipment, it is attractive to lift the reel and the power stand separately from each other. This reduces the weights of the individual lifts and allows for a heavier coiled tubing reel to be lifted onto the rig, if desired. However, this means that the load carrying components of the lifted equipment must be certified to multiple lifting standards in order to account for the wide range of weights that the equipment will weigh when lifted together as opposed to individually.
Typical DNV 2.7-1 skids, such as the skid shown in FIGS. 1A-1B, have an outer crash frame 100 surrounding a coiled tubing reel 105 and a power stand 106. As shown in FIG. 1B, the outer crash frame 100 is also the load carrying structure when the frame 100 is lifted. That is, the crash frame 100 is lifted by attaching cables 102 to four eyelets 104 at the corners of the frame 100, and applying a lift force FL to the cables 102. As such, the entire crash frame 100 is load carrying, and therefore, each of its components must meet the applicable DNV standards.
For example, the entire frame 100 must be composed of members not less than 0.25″ thick (the minimum thickness to Charpy test) and it must have a very large span to go around the items to be enclosed (such as the coiled tubing reel 105 and the power stand 106.) Further, this crash frame 100 often gets in the way of actually using the contents (the reel 105 and stand 106) of the skid. This means that the frame 100 must have removable components to allow access to the reel 105, adding a large number of joints that must be vastly over-designed to meet the certification requirements of the appropriate DNV standard.
Accordingly, a need exists for a method of lifting coiled tubing equipment that reduces the costs of complying with DNV lifting standards, such as DNV 2.7-1, DNV 2.7-3 and/or RCLA.